Kentico uses the Lucene.Net search engine, exact scoring calculation is complex.
You can find some info here:
Some things to remember that influencing score:
- number of occurences of the term
- if its in the document name or in the content, meta data
- if its just mentioned once in a lot of content or multiple times in short content
If you go to the search preview of your index you can see the results from the default transformation:
Hope this helps you and your customer understand.